This invention relates to the cooling of internal combustion engines and, more particularly, to the cooling of marine engines.
In the past, various types of cooling systems have been employed for marine engines, including, for example, systems which merely pump coolant in an uncontrolled manner through engine cooling passages, so-called blocking systems which employ a thermostatic valve for blocking coolant flow through the engine cooling passages until the coolant has reached a predetermined level, and recirculating systems which recirculate the coolant through engine cooling passages until the predetermined coolant temperature is reached, after which some of the warm coolant overflows and sufficient make-up coolant is introduced to maintain the coolant at the predetermined temperature.
For optimum engine performance under idling speed conditions, it is desirable for the areas of the engine in the vicinity of the cylinders to be relatively warm. This condition assists in maintaining smooth engine operation and preventing spark plug fouling, which is particularly advantageous for two-cycle engines employing a fuel containing a lubricating oil. Under high speed conditions, optimum engine performance is obtained by maintaining the cylinders as cool as possible. Although providing satisfactory cooling at some engine speeds, the above-described cooling systems do not provide optimum cooling throughout the entire range of engine speeds.
U. S. Kueny et al U.S. Pat. No. 3,667,431, issued June 6, 1972, describes an improved cooling system having separate coolant jacket portions. The primary flow of coolant from one coolant jacket portion to the other is selectively controlled by thermostatic valve and/or pressure relief valve. The thermostatic valve prevents coolant flow until the temperature of the coolant in the first coolant jacket portion has reached a predetermined level and, if used, the pressure relief valve opens to afford coolant flow when the pressure of the coolant in the first coolant jacket portion reaches a predetermined level.